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© 2011 Office of STEM Education Partnerships, Northwestern University Balanced & Unbalanced Forces – Teacher Overview – 3 pages
Balanced and Unbalanced Forces
Lesson Created by
Carlos Irizarry, George B. Swift Specialty School, Chicago, Illinois
Purpose
To fully appreciate and make a connection to Newton’s Laws, students must explore how unbalanced forces cause an object to move. Students must also be able to quantify force to better understand the nature of balanced and unbalanced forces.
Overview
Students will use the Fourier force meters to investigate the net force of a sliding block and observe how greater unbalanced force results in greater motion. Students will also observe how balanced opposing forces create net zero force which results with zero motion.
Students may also explore how greater or lesser weight of an object requires greater or lesser force to move that object. Using the HP force meter and tablets, students are able to record their observations quantitatively. Students also develop force diagrams to publish their findings.
Student Outcomes
Illinois State Standards:
• 11.A.3c: Collect and record data accurately using consistent measuring and recording techniques and media.
• 11.A.3f: Interpret and represent results of analysis to produce findings. • 12.D.3a: Explain and demonstrate how forces affect motion.
National Science Education Standards:
• 8ASI1.3: Use appropriate tools and techniques to gather, analyze, and interpret data. The use of tools and techniques, including mathematics, will be guided by the question asked and the investigations students design. The use of computers for the collection, summary, and display of evidence is part of this standard. Students should be able to access, gather, store, retrieve, and organize data, using hardware and software designed for these purposes.
• 8ASI2.4: Technology used to gather data enhances accuracy and allows scientists to analyze and quantify results of investigations.
• 8BPS2.1: The motion of an object can be described by its position, direction of motion, and speed. That motion can be measured and represented on a graph.
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© 2011 Office of STEM Education Partnerships, Northwestern University Balanced & Unbalanced Forces – Teacher Overview – 3 pages
Time
One 45-‐minute class period Level
8th Grade Physical Science Materials and Tools
• HP tablet computer
• HP 39gs graphing calculator emulator software • HP force meter (DT272)
• HP StreamSmart 400 • Multiple weighted blocks • Rubber bands
• String, yarn, etc.
Preparation
• Test all force meters and HP tablets and make certain they are operational. • Ensure that there are enough materials available to students to support student
autonomy.
• Students will need a large, flat working surface. Prerequisites
• Students should have a working understanding of forces, friction, weight, gravity, and resistance.
• Force diagrams should have been modeled and practiced prior to this activity. Background
Students should also be well trained in using the HP force meter and gathering data on the HP tablets.
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© 2011 Office of STEM Education Partnerships, Northwestern University Balanced & Unbalanced Forces – Teacher Overview – 3 pages
Teaching Notes
• A class tug-‐o-‐war activity can be a very fun and powerful activity to help solidify their budding understanding of these concepts.
• Weighted blocks can be substituted for any other materials that have some weight and small resistance to moving.
This work is supported by a grant from Hewlett-‐Packard under the HP Catalyst Initiative. However, any opinions, findings, conclusions and/or recommendations are
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© 2011 Office of STEM Education Partnerships, Northwestern University Balanced & Unbalanced Forces – Student Guide – 3 pages
Balanced and Unbalanced Forces
Review:
It is important to remember that force can be described as a push or a pull. When
one object pushes or pulls a second object, one can say that the first object is
exerting a force upon the second object. Much like when a soccer player kicks a
soccer ball, the soccer player (the first object) kicks the ball (the second object)
thereby exerting a force onto it. You exert a force whenever you lift, turn, carry,
or throw something. You exert a force even when standing still!
Remember: what’s the force that is always exerted upon us while we are on
Earth? We try to resist this force every time we stand, walk, run, climb, etc.
Remember also our discussion on balanced and unbalanced forces. When the
forces put upon an object are balanced, the forces will not change the object’s
motion. However, when the forces are unbalanced the object’s motion will
change. Remember net zero force means zero change in motion.
How is standing still an example of forces in balance? How is falling downstairs an
example of forces that are unbalanced? Do NOT demonstrate!
Challenge:
Today we will explore how an object’s mass, the force(s) exerted upon it, and the
changes in its motion are all interrelated.
Think aloud with your group…
Does the amount of force exerted upon an object affect its motion?
How does changing the mass/weight of the object affect the amount of force
needed to set the object in motion?
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© 2011 Office of STEM Education Partnerships, Northwestern University Balanced & Unbalanced Forces – Student Guide – 3 pages
Procedure 1:
1. Place one block upon the table, and hook two force meters to it (one to
each side as previously demonstrated).
2. Two group members should each take a force meter and pull the block so
that it reads 1 N on each meter.
3. Observe the block. In your science notebook, draw a force diagram similar
to the example below. On your force diagram record the forces on the
block from Step 2. Discuss with your team and explain in your notes why
the block is not in motion.
4. Have one group member gently pull the block with the force meter at 1.5
N, while the other group member pulls steady with the force meter staying
at 1 N.
5. Observe the block. In your science notebook, draw another force diagram.
On your force diagram record the forces on the block from Step 4. Discuss
with your team and explain in your notes why the block IS in motion.
6. Give other members of your team the opportunity to carry out Step 4 and
observe changes in motion with changes of force.
7. Discuss with your group: Does the amount of force applied to the block
change its motion (direction and speed)? Draw conclusions and record your
group’s thoughts in your notes.
8. Discuss with your group: Which force diagram should be labeled “Zero Net
Force”? Which force diagram should be labeled “Non-‐zero Net Force”?
Which diagram shows balanced forces? Which diagram shows unbalanced
forces?
9. Label each diagram accordingly.
Force Diagram Template
Block
____N
____N
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© 2011 Office of STEM Education Partnerships, Northwestern University Balanced & Unbalanced Forces – Student Guide – 3 pages
